Utils

Will attempt to evaluate a string expression and will catch any exception. For use in circumstances when logging is needed (i.e. a fatal error has already occurred and we need to log as much info as possible (i.e. put as much info as possible in the 'black box'). Also used to allow dumping (ex. for logging) a Query AST before it is completely built.

visitor will get applied on a proxied Sample object of the Queryable[A], this function is used for obtaining AST nodes or metadata from A.